The invention relates to a use of an apparatus for converting a rotary motion into an axial motion or vice versa.
FIGS. 1a and 1b show, in section and plan view respectively, a spindle 1, which by way of example may be the end of a drive motor shaft. Provided on the spindle 1 is preferably a simplex fine thread 10, which in turn has a pitch S of 0.3 to 0.25 mm or less.
Also, a number of rollers or roller bodies 3a-3f, for instance six, which are shown in FIG. 1a in section and in FIG. 1b in plan view, are disposed in the mounted state of the spindle arrangement in planetlike fashion between the spindle 1 and a nut 2. A correspondingly finely embodied groove contour 31, comprising grooves of a certain spacing extending next to one another and parallel, is also provided on predetermined segments on the rollers or roller bodies 3a-3f. The groove contour 31 facing toward the spindle 1 that will hereinafter be called the spindle-side contour. Because of this constant groove spacing and the groove depth, an exact engagement with the thread 10 of small pitch on the spindle 1 is assured.
Between the segments formed on the individual rollers or roller bodies 3a-3f, coarse guide grooves 32 of V-shaped cross section are also formed, which will hereinafter be called the nut-side contour. The spacing of the guide grooves 32 is exactly the same as that of guide grooves 20, which are formed in the interior of the spindle nut 2. The guide grooves 20 are also of V-shaped cross section, and mate with the guide grooves 32 of the roller or roller bodies 3 (i.e., 3a-3f).
In order that all the rollers or roller bodies 3 will mesh exactly and reliably both with the nut-side groove contour of a certain spacing in the interior of the nut 2 and with the spindle 1 of small thread pitch, the spindle-side groove contour 31 on each of the planetary rollers is disposed with a specific pitch offset that is constant from roller to roller and is fixed as a function of the total pitch to be attained.
In this way the rollers or roller bodies 3a-3f in the intended intermediate segments each has a different pitch offset, with respect to the fine contour 31. The rollers 3 must therefore be disposed in a very specific order, to which end a suitable identification is provided on individual rollers 3, for instance on the face end.
When the pitch of the fine thread on the spindle 1 is 0.3, for instance and with a corresponding spacing of the groove pitch, this would mean a pitch offset or displacement of 0.05 mm from one roller to another, or expressed in degrees, 60xc2x0 of angle between each pair of the six illustrated rollers 3a-3f. Or expressed in another way, when counting begins at a certain roller, the pitch offset of the contour 31 of the nth roller is equal to the product of the (number of the particular roller of interest xe2x88x921)xc3x97360xc2x0/total number of rollers.
In an alternate, second embodiment, the planetary rollers are provided with a thread of positive or negative pitch and the spindle is analogously provided with grooves. The nut-side guide grooves of the rollers and the corresponding guide grooves of the nut remain as described above. However, in the second embodiment a cage is necessary that keeps the planetary rollers spaced apart angularly from one another.
Such an apparatus for converting a rotary motion into an axial motion is described in U.S. Pat. No. 4,926,708, the contents of which are incorporated herein by reference.
According to the invention, such an apparatus for converting a rotary motion into an axial motion and vice versa is used for overload protection.
In accordance with an advantageous further feature of the invention, the apparatus used for converting a rotary motion into an axial motion is further embodied such that the force transmitting elements, namely the threaded spindle, the nut and/or the rollers or roller bodies having the various contours are made from deformable, preferably elastically deformable material. The elastically deformable material of the force transmitting elements is preferably polymer material or suitable deformable or elastically deformable materials.
Thus if in the known apparatus for converting a rotary motion into an axial motion the force transmitting elements, especially the rollers or roller bodies with the different contours, are made of deformable or elastically deformable material, such as a polymer and the like, a system pitch change dependent on the load is obtained that can be used and exploited as overload protection. Such a system pitch change can also be established not only as a function of load but also via the rpm and the prestressing of the entire spindle system. This in turn means that if there is major prestressing in the low rpm, a greater force transmission results, with attendant major protection against overload.